WO2010026678A1 - Hydraulic control system in working machine - Google Patents

Abstract

A hydraulic control system in a working machine, configured such that the potential energy of a vertically moving working section is recovered and stored as pressure into an accumulator, wherein the accumulator is adapted to be able to store pressurized oil having a high pressure capable of coping with work under a high load. A hydraulic control system in a working machine is provided with an openable and closable unload oil path (first head-side oil path (19), first flow rate control valve (33), head-side oil discharge path (40), and unload valve (41)) for allowing pressurized oil in a head-side oil chamber of a first boom cylinder, among a pair of first and second boom cylinders (8, 9) for lifting and lowering a working section (4), to flow to an oil tank (12).  The hydraulic control system is configured such that, when lifting and lowering motion of the working section is being stopped and when the working section is lifted, the unload oil path is closed to cause the pressure in head-side oil chambers of the first and second boom cylinder to hold the weight of the working section and such that, when the working section is lowered, the unload oil path is opened to cause the pressure in the head-side oil chamber of the second boom cylinder to hold the weight of the working section.  The hydraulic control system is also provided with an accumulator (59) which, when the working section is lowered, stores the pressure of oil discharged from the head-side oil chamber of the second boom cylinder.

Description

Hydraulic control system in work machine

The present invention belongs to the technical field of a hydraulic control system in a working machine capable of recovering and reusing potential energy of the working unit in a working machine provided with a vertically movable working unit.

Generally, a working machine such as a hydraulic shovel or a crane is provided with a vertically movable working unit, and the working unit is configured to move up and down based on the expansion and contraction operation of a hydraulic cylinder supplied with pressure oil from a hydraulic pump In this case, oil discharged from the head-side oil chamber of the hydraulic cylinder to the oil tank during descent of the working unit is conventionally discharged to supply oil to the hydraulic cylinder in order to prevent it from falling sharply due to its own weight. Metering out control is configured by a throttle provided on a control valve that performs control. That is, although the working unit located above the ground has potential energy, the potential energy is converted into heat energy when passing through the throttle of the control valve, and the heat energy is an oil cooler Will be released to the atmosphere, resulting in unnecessary energy loss.
Therefore, in order to recover and reuse potential energy of the working unit, an assist cylinder is provided in addition to the conventionally provided hydraulic cylinder, and the oil discharged from the head-side oil chamber of the assist cylinder when the working unit descends. Patent Document 1 discloses a technology in which pressure is accumulated in an accumulator and pressure oil accumulated in the accumulator is supplied to a head-side oil chamber of an assist cylinder when the working unit ascends (see, for example, Patent Document 1).
However, although the discharge oil from the assist cylinder is accumulated in the accumulator at the time of descent of the working part in the Patent Document 1, the discharged oil from the hydraulic cylinder conventionally provided for raising and lowering the working part is The oil is discharged to the oil tank via the control valve, and only a part of the potential energy of the working machine is recovered. Moreover, when the working part is elevated, a part of the pressure oil supplied from the hydraulic pump to the hydraulic cylinder via the control valve is supplied to the assist cylinder when the accumulator is not sufficiently accumulated in the accumulator and for accumulator accumulator pressure As a result, the rising speed of the working unit is slowed and the working efficiency is reduced.
On the other hand, without providing the assist cylinder, while accumulating the oil discharged from the hydraulic cylinder at the time of descent of the working unit in the accumulator, at the same time of supplying the pressure oil accumulated in the accumulator at the time of ascending the working unit to the hydraulic cylinder In this case, the potential energy of the working machine can be recovered with certainty, but in this case, the pressure of the accumulator oil is not higher than the holding pressure at which the hydraulic cylinder holds the weight of the working part. The pressure of the hydraulic oil used during high load operation may be insufficient. Therefore, a technology has been proposed in which the pressure-accumulated oil of the accumulator is increased to a high pressure by a dedicated pump driven by engine power and supplied to a hydraulic cylinder (see, for example, Patent Document 2).

Patent No. 2582310 JP 2008-14468 A

However, in the case of Patent Document 2, a dedicated pump for increasing the pressure accumulated in the accumulator to a high pressure, and a power transmission device (gear device etc.) for transmitting the engine power to the pump become necessary, resulting in an increase in cost. In addition, there is a problem of energy loss such as torque reduction in power transmission equipment and idling torque due to inertia mass of the pump itself, so that further energy saving is required, and the present invention is intended to solve the problem. There is a problem.

The present invention has been made to solve these problems in view of the above situation, and the invention according to claim 1 comprises a vertically movable work unit, and a pair of vertically movable work units. In a hydraulic control system of a working machine comprising a first and a second hydraulic cylinder, the hydraulic control system includes an openable and closable unload oil passage for flowing pressure oil in a head side oil chamber of the first hydraulic cylinder to an oil tank A controller for controlling the opening and closing of the unloading oil passage, and holding the weight of the working part by the pressure of the head side oil chamber of the first and second hydraulic cylinders in a state where the unloading oil passage is closed; The first and second embodiments are configured to hold the weight of the working unit by the pressure of the head side oil chamber of the second hydraulic cylinder when the unloading oil passage is open, and to hold the weight when the working unit is lowered. Or second hydraulic system A hydraulic control system in a working machine, characterized in that a accumulator for accumulating oil discharged from the head-side oil chamber of Sunda.
According to the second aspect of the present invention, the hydraulic control system is controlled by the control device to open and close the head side communication oil path connecting the head side oil chambers of the first and second hydraulic cylinders and the head side communication oil path. And the control device opens the head side communication oil passage in the state where the unloading oil passage is closed, while the control device is configured to open the head communication passage. The hydraulic control system in a working machine according to claim 1, characterized in that control is performed so as to close the head side communication oil passage in a state in which the valve is open.
The invention according to claim 3 is characterized in that the control device controls to open the unloading oil passage when the working unit is lowered, and close the unloading oil passage when the elevation of the working unit is stopped and when the work unit is lifted. It is a hydraulic control system in the working machine according to or 2.
The invention according to claim 4 is that the hydraulic control system includes an accumulator pressure detection means for detecting the pressure of the accumulator, and a first and a second head side pressure for detecting the pressures of the head side oil chambers of the first and second hydraulic cylinders, respectively. While the detection means is provided, the control device sets in advance the differential pressure between the average pressure of the head side oil chambers of the first and second hydraulic cylinders and the pressure of the accumulator even when the working unit is lowered. The hydraulic control system in a working machine according to claim 3, wherein the unloading oil passage is controlled to be closed when the set value or more.
The invention according to claim 5 is that the second head side pressure detecting means for detecting the pressure in the head side oil chamber of the second hydraulic cylinder and the second relief for setting the head side relief pressure of the second hydraulic cylinder in the hydraulic control system. In addition to providing a valve, the control device sets in advance the differential pressure between the head-side relief pressure of the second hydraulic cylinder and the pressure of the head-side oil chamber of the second hydraulic cylinder even when the working unit is lowered. The hydraulic control system in a working machine according to claim 3 or 4, characterized in that the unloading oil passage is controlled to be closed when the pressure value is less than the set value.
The invention according to claim 6 is that the hydraulic control system is provided with first and second flow control valves for controlling the discharge flow from the head-side oil chamber of the first and second hydraulic cylinders when the working unit is lowered. It is a hydraulic control system in a working machine according to any one of claims 1 to 5 characterized by the above.
The invention according to claim 7 relates to the hydraulic control system, the flow of oil from the head side oil chamber of the first and second hydraulic cylinders to the accumulator, and the oil from the accumulator to the head side oil chamber of the first and second hydraulic cylinders The hydraulic control system in a working machine according to any one of claims 1 to 6, further comprising: valve means capable of blocking the flow of water.
The invention according to claim 8 relates to the hydraulic control system, accumulator pressure detection means for detecting the pressure of the accumulator, and first and second head side pressures for detecting the pressures of the head side oil chambers of the first and second hydraulic cylinders, respectively. A detection means, an openable / closable tank oil passage for flowing oil discharged from the head side oil chamber of the first and second hydraulic cylinders to the oil tank via the first and second flow rate control valves, and the first and second oil passages A control means is provided with a valve means capable of blocking the flow of oil from the head side oil chamber of the hydraulic cylinder to the accumulator and the flow of oil from the accumulator to the head side oil chamber of the first and second hydraulic cylinders. When the pressure of the head side oil chamber of the first and second or second hydraulic cylinder holding weight is smaller than the pressure of the accumulator when the working part is lowered, the valve means The oil flow from the head side oil chamber of the pressure cylinder to the accumulator and the oil flow from the accumulator to the head side oil chambers of the first and second hydraulic cylinders are blocked, and the tank oil passage is opened. The hydraulic control system according to claim 6, wherein the pressure oil in the head side oil chamber of the second hydraulic cylinder is caused to flow to the oil tank via the first and second flow control valves.

According to the invention of claim 1, when the working part is lowered, the unloading oil passage is opened and the pressure oil in the head side oil chamber of the first hydraulic cylinder flows to the oil tank so that the weight of the working part is the second The pressure is maintained at the pressure of the head side oil chamber of the hydraulic cylinder, and the oil discharged from the head side oil chamber of the second hydraulic cylinder is accumulated in the accumulator. In this case, the head side of the second hydraulic cylinder Since the pressure in the oil chamber, that is, the holding pressure for holding the weight of the working unit is doubled with respect to the holding pressure when holding the weight of the working unit with both the first and second hydraulic cylinders, A high pressure hydraulic oil which can cope with high load operation is accumulated, and therefore, the accumulator oil of the accumulator can be used for various operations without using additional pressure increase. Furthermore, as in the case of increasing the pressure-accumulating oil of the accumulator using a pump driven by the engine power, there is no loss of torque in the power transmission path from the engine to the pump or loss of idling torque due to inertial mass of the pump itself. The potential energy of the working unit collected in the accumulator can be used with as little loss as possible, and can greatly contribute to cost reduction.
According to the second aspect of the invention, in the state where the unloading oil passage is closed, that is, in the state where the weight of the working portion is held by the head side oil chambers of the first and second hydraulic cylinders, The head-side oil chambers of the second hydraulic cylinder are in communication with each other, and the first and second hydraulic cylinders can support the working unit in a well-balanced manner, while the unloading oil passage is open, that is, the second hydraulic cylinder In the state in which the weight of the working unit is held by the head side oil chamber of the above, it is possible to shut off the head side oil chamber of the second hydraulic cylinder and the head side oil chamber of the first hydraulic cylinder.
According to the invention of claim 3, the unloading oil passage is opened, that is, the weight of the working unit is held by the second hydraulic cylinder at the time of lowering of the working unit for accumulating pressure in the accumulator. At the time of lifting stop and lifting of the unit, the unloading oil passage is closed, that is, the weight of the working unit is held by the first and second hydraulic cylinders, so except during the descent of the working unit for accumulating pressure in the accumulator. The loss of flowing pressure oil from the head side oil chamber of the first hydraulic cylinder to the oil tank can be eliminated at the same time, and when the working part is raised, the power will be insufficient or the balance will be lost. There is no excuse.
According to the invention of claim 4, unloading is performed when the pressure on the head side oil chamber of the first and second hydraulic cylinders is high relative to the pressure of the accumulator even when the working unit is lowered. The oil passage is closed, and the pressure of the head side oil chamber of the first and second hydraulic cylinders holds the weight of the working part, and the oil discharged from the head side oil chamber of the first and second hydraulic cylinders serves as an accumulator. It is possible to reduce the loss of flowing pressure oil in the head side oil chamber of the first hydraulic cylinder to the oil tank by opening the unloading oil passage.
According to the fifth aspect of the present invention, even when the working unit descends, the unloading oil is used when the differential pressure between the head side relief pressure of the second hydraulic cylinder and the pressure of the head side oil chamber becomes equal to or less than the set value. The passage is closed, and the weight of the working unit is held by the first and second hydraulic cylinders, whereby the pressure in the head-side oil chamber of the second hydraulic cylinder rises excessively and the second head-side relief valve It can prevent that it operates.
According to the sixth aspect of the present invention, the lowering speed of the working unit can be controlled by the first and second flow control valves.
According to the invention of claim 7, the flow of oil from the head side oil chamber of the first and second hydraulic cylinders to the accumulator by the valve means, and the first and second hydraulic cylinders from the accumulator when the elevation of the working unit is stopped. The pressure oil in the head side oil chambers of the first and second hydraulic cylinders may flow out to the accumulator, or the pressure accumulation oil in the accumulator may become the first and second oil pressure, by blocking the flow of oil into the head side oil chamber of the It is possible to reliably avoid such a problem that the oil is supplied to the head side oil chamber of the cylinder.
According to the invention of claim 8, when the pressure of the head side oil chamber of the first and second or second hydraulic cylinder holding the weight of the working unit is lower than the pressure of the accumulator when the working unit is lowered. The valve means can prevent oil from flowing backward from the accumulator to the head side oil chambers of the first and second hydraulic cylinders, and even in this case, the speed control by the first and second flow control valves In the closed state, the working unit can be lowered.

It is a perspective view of a hydraulic shovel. FIG. 2 is a hydraulic circuit diagram of a hydraulic control system. It is a block diagram which shows the input-output of a control apparatus. It is a flowchart figure which shows judgment of cantilever control and both-ends control.

Next, embodiments of the present invention will be described based on the drawings. In FIG. 1, reference numeral 1 denotes a hydraulic shovel, which is an example of a working machine, and the hydraulic shovel 1 is a crawler type lower traveling body 2 and an upper revolving structure 3 rotatably supported above the lower traveling body 2. The boom 5 includes a working unit 4 and the like attached to the front of the upper swing body 3, and the working unit 4 further includes a boom 5 whose base end portion is supported by the upper swing body 3 so as to be vertically pivotable. The arm 6 is supported at the front end of the boom 5 so as to be pivotable back and forth, and the bucket 7 and the like attached to the front end of the arm 6.

Further, 8 and 9 are a pair of left and right first and second boom cylinders (corresponding to the first and second hydraulic cylinders of the present invention) for swinging the boom 5 up and down. The two boom cylinders 8, 9 hold the weight of the working unit 4 by the pressure of the head side oil chambers 8a, 9a, and supply pressure oil to the head side oil chambers 8a, 9a and from rod side oil chambers 8b, 9b. Discharge the oil by moving the boom 5 upward, and supply the pressure oil to the rod side oil chambers 8b, 9b and the oil discharge from the head side oil chambers 8a, 9a reduce the boom 5 so as to lower it. It is configured. The entire working unit 4 ascends and descends as the boom 5 ascends and descends, and the potential energy of the working unit 4 increases as the boom 5 ascends, but the potential energy is recovered by a hydraulic control system described later. Are to be reused. The first boom cylinder 8 is one of the boom cylinders 8 and 9, and the second boom cylinder 9 is the other boom cylinder 9, and in FIG. Although one boom cylinder 8 is used and the right side is used as the second boom cylinder 9, it may be of course reversed.

Next, the hydraulic control system will be described based on the hydraulic circuit diagram of FIG. 2. In FIG. 2, 8 and 9 indicate the first and second boom cylinders, and 10 indicates the engine E mounted on the hydraulic shovel 1. A variable displacement main pump to be driven, 11 a pilot pump serving as a pilot hydraulic pressure source, and 12 an oil tank. The main pump 10 is not only the first and second boom cylinders 8 and 9 but also a plurality of other hydraulic actuators (not shown in FIG. 2 but traveling motors, swing motors, arms) provided in the hydraulic shovel 1 It is a hydraulic pump which becomes an oil pressure supply source of a cylinder, a bucket cylinder, etc.).

Further, reference numeral 13 denotes a regulator for controlling the discharge flow rate of the main pump 10. The regulator 13 receives the control signal pressure from the main pump output control electromagnetic proportional pressure reducing valve 14 and controls the engine speed and the work load. While operating to obtain a corresponding pump output, constant horsepower control is performed by receiving the discharge pressure of the main pump 10. Furthermore, although the regulator 13 also performs flow control based on the negative control signal pressure Pn or the flow control signal pressure Pc, the flow control will be described later.

On the other hand, 15 is a discharge line of the main pump 10, and the discharge line 15 merges with a joining oil passage 16 described later and reaches a pressure oil supply oil passage 17, and the pressure oil supply oil passage 17 A boom cylinder control valve 18 is connected to perform oil supply and discharge control to the first and second boom cylinders 8 and 9. Further, a hydraulic actuator control valve (traveling motor (hydraulic motor control valve) performing oil supply and discharge control not only to the boom cylinder control valve 18 but also to a plurality of other hydraulic actuators provided in the hydraulic shovel 1 in the pressure oil supply oil passage 17 Control valves, a control valve for the swing motor, a control valve for the arm cylinder, a control valve for the bucket cylinder, etc. are also connected, but are omitted in FIG.

The boom cylinder control valve 18 is constituted by a spool valve provided with rising side and lowering side pilot ports 18a and 18b, and the first, second, and third pilot valves 18a and 18b are not used. It is located at the neutral position N where the oil supply and discharge to the second boom cylinders 8 and 9 is not performed, but when the pilot pressure is input to the rising side pilot port 18a, the pressure oil in the pressure oil supply oil passage 17 is First, the head side oil chambers 8a and 9a of the second boom cylinders 8 and 9 are switched to the rising side position X in which the oil discharged from the rod side oil chambers 8b and 9b is supplied to the oil tank 12 The pressure oil in the pressure oil supply oil passage 17 is set to the rod side oil of the first and second boom cylinders 8 and 9 by the pilot pressure being input to the lowering side pilot port 18b. 8b, and is configured to Setsu換Ru so the descending side position Y to be supplied to 9b.

Here, the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 and the control valve 18 for the boom cylinder are the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9, respectively. Through the first and second head side oil passages 19 and 20 respectively connected to the head side oil chambers 8a of the first and second boom cylinders 8 and 9 through the first and second head side oil passages 19 and 20, respectively. 9a are connected with each other via a head side communication oil passage 21 which communicates with each other, and a head side main oil passage 22 which connects the head side communication oil passage 21 and the boom cylinder control valve 18 with each other. The rod side oil chambers 8b and 9b of the first and second boom cylinders 8 and 9 and the boom cylinder control valve 18 communicate with rod side communication oil passages 23 communicating the rod side oil chambers 8b and 9b with each other, and It is connected via a rod-side main oil passage 24 connecting the rod-side communication oil passage 23 and the boom cylinder control valve 18. Thus, oil is supplied and discharged between the first and second boom cylinders 8 and 9 and the boom cylinder control valve 18 through these oil passages.

On the other hand, 25 and 26 are rising side and falling side electromagnetic proportional pressure reducing valves, and these electromagnetic proportional pressure reducing valves 25 and 26 are the boom cylinder control valve 18 based on a control signal from the control device 27 described later. The pilot pressure is operated to output the pilot pressure to the rising side pilot port 18a and the lowering side pilot port 18b, respectively. The pilot pressures output from the rising side and the lowering side electromagnetic proportional pressure reducing valves 25 and 26 are controlled to increase or decrease according to the operation amount of the boom control lever (not shown), and the pilot pressure is increased or decreased. The opening area of the boom cylinder control valve 18 is controlled to be increased or decreased by increasing or decreasing the moving stroke of the spool correspondingly to the first and second boom cylinders from the boom cylinder control valve 18. It is comprised so that increase / decrease control of the supply-and-discharge flow rate to 8,9 may be made | formed.

Further, the boom cylinder control valve 18 is formed with a center bypass valve passage 18 c for flowing the pressure oil of the pressure oil supply oil passage 17 to the oil tank 12 via the negative control valve 28. The passage flow rate of the center bypass valve passage 18c is largest when the boom cylinder control valve 18 is at the neutral position N, and becomes smaller as the movement stroke of the spool becomes larger, that is, the operation amount of the boom control lever increases. The flow rate of the center bypass valve 18 c is controlled to decrease. Then, the passing flow rate of the center bypass valve passage 18c is output to one input port 29a of a shuttle valve 29 described later as a negative control signal pressure Pn.

Reference numeral 30 denotes a main pump flow control electromagnetic proportional pressure reducing valve that outputs a flow control signal pressure Pc based on a control signal from the control device 27, and is output from the main pump flow control electromagnetic proportional pressure reducing valve 30. The flow control signal pressure Pc is input to the other input port 29 b of the shuttle valve 29.

The shuttle valve 29 selects the high pressure side out of the negative control signal pressure Pn and the flow control signal pressure Pc input from the input ports 29a and 29b, and outputs the same to the regulator 13 of the main pump 10. Then, the regulator 13 controls the flow rate of the main pump 10 so as to decrease the pump flow rate as the input signal pressure is higher. That is, of the negative control signal pressure Pn and the flow control signal pressure Pc, the signal pressure for reducing the discharge flow rate of the main pump 10 is selected by the shuttle valve 29 and is input to the regulator 13. When the negative control signal pressure Pn is input, the pump flow rate is increased or decreased according to the increase or decrease of the operation amount of the boom control lever, while when the flow control signal pressure Pc is input, the flow rate control Although flow control based on the signal pressure Pc is performed, this flow control signal pressure Pc will be described later.

On the other hand, the first and second head side oil passages 19, 20 are oil passages connected to the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 as described above, The first and second head side oil passages 19 and 20 allow oil supply to the head side oil chambers 8a and 9a but prevent oil discharge from the head side oil chambers 8a and 9a. The check valves 31, 32 and first and second flow control valves 33, 34 for controlling the flow rate of discharge from the head side oil chambers 8a, 9a are arranged in parallel. Thus, the oil supply to the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 is performed via the first and second check valves 31, 32, while the head side oil chamber 8a is , 9a are discharged via the first and second flow control valves 33, 34.

The first and second flow control valves 33, 34 are spool valves provided with pilot ports 33a, 34a, and in a state where pilot pressure is not input to the pilot ports 33a, 34a, the first and second heads It is located at the closed position N for closing the side oil passages 19 and 20. However, when the pilot pressure is input to the pilot ports 33a and 34a, the open position X for opening the first and second head side oil passages 19 and 20 It is comprised so that it may switch.

Reference numerals 35 and 36 denote first and second electromagnetic proportional pressure reducing valves, and the electromagnetic proportional pressure reducing valves 35 and 36 are controlled by the first and second flow rate control valves based on control signals from the controller 27. It operates to output pilot pressure to the pilot ports 33a, 34a of 33, 34. Then, the opening areas of the first and second flow control valves 33 and 34 are controlled to increase or decrease in response to the increase or decrease of the pilot pressure output from the first and second electromagnetic proportional pressure reducing valves 35 and 36. ing.

Furthermore, 37 and 38 are first and second relief valves connected to the first and second head side oil passages 19 and 20, respectively. The first and second relief valves 37 and 38 The head-side relief pressure of the second boom cylinders 8 and 9 is set.

On the other hand, as described above, the head side communication oil passage 21 is connected between the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 via the first and second head side oil passages 19 and 20, respectively. The head side communication oil path 21 is provided with a head side communication oil path opening / closing valve 39 for opening and closing the head side communication oil path 21 based on a control signal from the control device 27. ing. Thus, the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 are located at the open position X where the head side communication oil path opening / closing valve 39 opens the head side communication oil path 21. In the state, the communication is made via the first and second head side oil passages 19 and 20, but the head side communication oil passage on-off valve 39 is located at the closed position N closing the head side communication oil passage 21. Is configured to be in a blocked state. The on-off valve such as the head-side communication oil passage on-off valve 39 is not disposed in the rod-side communication fluid passage 23, and the rod- side oil chambers 8b and 9b of the first and second boom cylinders 8 and 9 Is always in communication.

Further, reference numeral 40 denotes a head-side discharge oil passage extending from the first head-side oil passage 19 to the oil tank 12, and an unload valve 41 is disposed in the head-side discharge oil passage 40. The second head-side oil passage 20 is connected to the head-side discharge oil passage 40 via the head-side communication oil passage 21, and the head-side communication oil passage on-off valve 39 is closed at the closed position N. In the state where the second head side oil passage 20 and the head side discharge oil passage 40 are shut off, the head side communication oil passage on-off valve 39 is positioned at the open position X. The oil of the second head side oil passage 20 can be made to flow to the head side discharge oil passage 40.

The unload valve 41 is configured using a poppet valve 42 and an electromagnetic switching valve 43 for unload valve that switches from the OFF position N to the ON position X based on a control signal output from the control device 27. . The unloading valve 41 blocks the flow of oil from the first head side oil passage 19 to the oil tank 12 when the unloading valve electromagnetic switching valve 43 is at the OFF position N, that is, the head It is held in the closed state to close the side discharge oil passage 40, but when the unload valve electromagnetic switching valve 43 is switched to the ON position X, the flow of oil from the first head side oil passage 19 to the oil tank 12 is That is, the head side discharge oil passage 40 is opened. Then, the pressure oil in the head-side oil chamber 8a of the first boom cylinder 8 is set to the first position by setting the unload valve electromagnetic switching valve 43 to the ON position X and opening the unload valve 41. It can be made to flow to the oil tank 12 via the one flow control valve 33 and the head side discharge oil passage 40. As described above, since the second head side oil passage 20 is connected to the head side discharge oil passage 40 via the head side communication oil passage 21, the head side communication oil passage on-off valve 39 is at the open position X. When the unloading valve 41 is open, the pressure oil of the head side oil chamber 9a of the second boom cylinder 9 is transferred to the oil tank via the second flow control valve 34 and the head side discharge oil passage 40. It is designed to be able to flow to twelve.

Here, as described above, when the unload valve 41 is in the open state, the pressure oil of the head side oil chamber 8 a of the first boom cylinder 8 is passed through the first flow control valve 33 and the head side discharge oil passage 40. In this case, by maximizing the opening area of the first flow control valve 33, the pressure oil in the head side oil chamber 8a of the first boom cylinder 8 is substantially unloaded. Can be flowed to the oil tank 12. In the present embodiment, the first head side oil passage 19, the first flow control valve 33, the head side discharge oil passage 40, and the unloading valve 41 constitute an openable / closable unload oil passage of the present invention. However, the state in which the unloading oil passage of the present invention is open means that the opening area of the first flow control valve 33 is the largest and the unloading valve 41 is in the open state, otherwise The unloading oil passage is closed.

Furthermore, 44 is a recovery oil passage connected to the second head side oil passage 20, and in the recovery oil passage 44, the head side oil of the second boom cylinder 8 passing through the second head side oil passage 20. Exhaust oil from the chamber 8a and exhaust oil from the head oil chamber 8a of the first boom cylinder 8 passing through the first head oil passage 19 and the head communication oil passage 21 are supplied. The passage 44 is connected to the accumulator oil passage 45 via a cylinder side check valve 46 and an accumulator side check valve 49 which will be described later. Here, the accumulator oil passage 45 is an oil passage connected to the accumulator 59 in order to supply and discharge pressure oil to the accumulator 59.

The cylinder side check valve 46 is configured by using a poppet valve 47 and a cylinder side check valve electromagnetic switching valve 48 that switches from the OFF position N to the ON position X based on a control signal output from the control device 27. ing. When the cylinder side check valve electromagnetic switching valve 48 is positioned at the OFF position N, the cylinder side check valve 46 is closed so as to block the flow of oil from the recovery oil passage 44 to the accumulator oil passage 45. However, when the cylinder side check valve electromagnetic switching valve 48 is switched to the ON position X, an open state allowing bidirectional flow between the recovery oil passage 44 and the accumulator oil passage 45 is established.

Further, the accumulator side check valve 49 uses the poppet valve 50 and the accumulator side check valve electromagnetic switching valve 51 that switches from the OFF position N to the ON position X based on the control signal output from the control device 27. It is configured. The accumulator side check valve 49 is in a closed state that prevents the flow of oil from the accumulator oil passage 45 to the recovery oil passage 44 when the accumulator side check valve electromagnetic switching valve 51 is in the OFF position N. However, when the accumulator side check valve electromagnetic switching valve 51 is switched to the ON position X, an open state allowing bidirectional flow between the recovery oil passage 44 and the accumulator oil passage 45 is established. The accumulator side check valve 49 allows the flow of oil from the recovery oil passage 44 to the accumulator oil passage 45 even when the accumulator side check valve electromagnetic switching valve 51 is in the OFF position N. However, when the accumulator side check valve electromagnetic switching valve 51 is at the ON position X, the pressure in the accumulator oil passage 45 is not introduced into the spring chamber 50a of the poppet valve 50, so recovery is performed with almost no pressure loss. Oil can flow from the oil passage 44 to the accumulator oil passage 45.

Thus, when the cylinder side check valve 46 and the accumulator side check valve 49 are both kept closed, the flow of oil from the recovery oil passage 44 to the accumulator oil passage 45 and the recovery from the accumulator oil passage 45 While the flow of oil to the oil passage 44 is both blocked, the head side oil chambers of the first and second boom cylinders 8, 9 are brought about by the cylinder side check valve 46 and the accumulator side check valve 49 both being opened. The exhaust oil from 8a, 9a can be accumulated in the accumulator 59 via the recovery oil passage 44 and the accumulator oil passage 45. The cylinder side check valve 46 and the accumulator side check valve 49 are the oil flow from the head side oil chamber of the first and second hydraulic cylinders to the accumulator and the first and second hydraulic cylinders of the accumulator. A valve means capable of blocking the flow of oil to the head side oil chamber is constituted. In the present embodiment, the accumulator 59 is a bladder type that is optimal for storing hydraulic energy. However, the accumulator 59 is not limited to this, and may be, for example, a piston type.

On the other hand, 16 is a combined oil passage formed from the accumulator oil passage 45 to the discharge line 15 of the main pump 10, and a combined valve 52 is disposed in the combined oil passage 16.

The merging valve 52 is an on-off valve that moves a spool based on the operation of a merging valve electro-hydraulic conversion valve 53 to which a control signal from the control device 27 is input. The merging valve electro-hydraulic conversion valve 53 is not In the state of operation, it is located at the closed position N where the merging oil passage 16 is closed, but the spool moves by the operation of the merging valve electrical oil conversion valve 53 to open the merging oil passage 16 to the open position X It is configured to switch. Furthermore, the merging valve 52 incorporates a check valve 54 that allows the flow of oil from the accumulator oil passage 45 to the discharge line 15 but blocks the flow in the reverse direction. Thus, by switching the joining valve 52 to the open position X, the pressure oil accumulated in the accumulator 59 is joined to the discharge line 15 of the main pump 10 via the accumulator oil passage 45 and the joining oil passage 16. It can be made to

The opening area of the merging valve 52 is controlled to increase or decrease according to the signal value of the control signal input from the control device 27 to the merging valve electric oil conversion valve 53, and the opening area of the merging valve 52 The control of increasing and decreasing the flow rate of the flow joining the discharge line 15 of the main pump 10 from the accumulator 59 via the merging oil passage 16 is performed by the increase and decrease control of

Further, 55 is a discharge oil passage for the accumulator which is branched from the accumulator oil passage 45 and reaches the oil tank 12, and a tank check valve 56 is disposed in the discharge oil passage 55 for the accumulator.

The tank check valve 56 is configured using a poppet valve 57 and a tank check valve electromagnetic switching valve 58 that switches from the OFF position N to the ON position X based on a control signal output from the control device 27. . The tank check valve 56 blocks the flow of oil from the accumulator oil passage 45 to the oil tank 12 when the tank check valve electromagnetic switching valve 58 is at the OFF position N, that is, the accumulator discharge oil Although the passage 55 is closed in a closed state, the tank check valve electromagnetic switching valve 58 is switched to the ON position X to allow the flow of oil from the accumulator oil passage 45 to the oil tank 12, that is, the accumulator The discharge oil passage 55 is opened. Then, by positioning the tank check valve electromagnetic switching valve 58 at the ON position X and opening the tank check valve 56, the accumulated oil of the accumulator 59 is oil via the accumulator discharge oil passage 55. It can be discharged into the tank 12.

On the other hand, the control device 27 is constituted by using a microcomputer or the like, and as shown in the block diagram of FIG. 3, a boom operation detection means 60 for detecting the operation direction and operation amount of the boom control lever; A pump pressure sensor 61 for detecting the discharge pressure of the main pump 10, and a first head pressure sensor for detecting the pressure of the head oil chamber 8a of the first boom cylinder 8 (equivalent to the first head pressure detection means of the present invention 62, a second head side pressure sensor (corresponding to the second head side pressure detecting means of the present invention) 63 for detecting the pressure of the head side oil chamber 9a of the second boom cylinder 9; A signal from an accumulator pressure sensor (corresponding to the accumulator pressure detection means of the present invention) 64 or the like is input, and based on these input signals, the above-mentioned Side electromagnetic proportional pressure reducing valve 25, Lower side electromagnetic proportional pressure reducing valve 26, Main pump flow rate controlling electromagnetic proportional pressure reducing valve 30, First electromagnetic proportional pressure reducing valve 35, Second electromagnetic proportional pressure reducing valve 36, Head side communication oil passage open / close valve 39 Control for unloading valve solenoid switching valve 43, cylinder side check valve solenoid switching valve 48, accumulator side check valve solenoid switching valve 51, merging valve electro-hydraulic conversion valve 53, tank check valve solenoid switching valve 58, etc. Output a signal.

Among the controls performed by the control unit 27, first, the cantilever control and the double-end control will be described. The control unit 27 operates the boom control lever input from the boom operation detection means 60, and the first head side pressure The pressure Ph1 of the head side oil chamber 8a of the first boom cylinder 8 input from the sensor 62, the pressure Ph2 of the head side oil chamber 9a of the second boom cylinder 9 input from the second head side pressure sensor 63, and an accumulator The weight of the working unit 4 is held by the pressure of the head side oil chambers 8a and 9a of both the first and second boom cylinders 8 and 9 based on the pressure Pa of the accumulator 59 input from the pressure sensor 64 Control the weight of the working unit 4 or the pressure of the head side oil chamber 9 a of the second boom cylinder 9 of one of the first and second boom cylinders 8 and 9. In determining whether to cantilever control to maintain.

That is, as shown in the flow chart of FIG. 4, the control device 27 determines whether the boom control lever is operated to the boom lowering side (step S1), the head side oil chambers of the first and second boom cylinders 8, 9 Whether the differential pressure between the average value ((Ph1 + Ph2) / 2) of the pressures Ph1 and Ph2 of 8a and 9a and the pressure Pa of the accumulator 59 is smaller than the preset value C1 ({(Ph1 + Ph2) / 2 } (Step S2), the difference between the head-side relief pressure Pr2 of the second boom cylinder 9 set by the second relief valve 38 and the pressure Ph2 of the head-side oil chamber 9a of the second boom cylinder 9 It is determined whether the pressure is larger than the preset value C2 set in advance (Pr2-Ph2> C2?) (Step S3), and all the determinations in steps S1, S2, and S3 are “Y In the case of S "it determines that performs control cantilevered, if even one of the" NO "is determined to perform the inboard control.

Then, when it is determined that the both-end control is to be performed in the determinations of the steps S1, S2 and S3, the control device 27 sets the control signal to the OFF position N with respect to the unload valve electromagnetic switching valve 43. Then, the unloading valve 41 is closed (closing the unloading oil passage). Further, the control device 27 outputs a control signal so as to be positioned at the open position X with respect to the head side communication oil passage open / close valve 39. As a result, the head side oil chambers 8 a and 9 a of the first and second boom cylinders 8 and 9 are in communication with each other via the first and second head side oil passages 19 and 20. In this state, both the first and second boom cylinders 8, 9 will be responsible for holding the weight of the working unit 4, so that the head side of both the first and second boom cylinders 8, 9 Both-end control for holding the weight of the working unit 4 is executed by the pressure of the oil chambers 8a and 9a.

On the other hand, when it is determined that the cantilever control is to be performed in the determinations of the steps S1, S2 and S3, the control device 27 sets the control signal to be located at the closed position N with respect to the head side communication oil passage open / close valve 39. Output. As a result, the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 are shut off. Furthermore, the control device 27 outputs a control signal of the maximum pilot pressure output to the first electromagnetic proportional pressure reducing valve 35 to maximize the opening area of the first flow control valve 33, and the electromagnetic switching valve 43 for unloading valve. Is output to the ON position X to open the unloading valve 41 (open the unloading oil passage). As a result, the oil in the head side oil chamber 8a of the first boom cylinder 8 flows to the oil tank 12 via the first head side oil passage 19 and the head side discharge oil passage 40, and the first boom cylinder The pressure of the head side oil chamber 8a of 8 decreases to substantially the tank pressure. In this state, weight retention of the working unit 4 by the first boom cylinder 8 is not performed, and only the second boom cylinder 9 is responsible for weight retention of the working unit 4, and thus, the first and second boom cylinders The cantilever control for holding the weight of the working unit 4 is executed by the pressure of the head-side oil chamber 9 a of one of the second boom cylinders 9 among 8 and 9. The pressure of the head-side oil chamber 9a of the second boom cylinder 9 is controlled by the above-mentioned cantilever control so that the head- side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 at the time of the double control. Pressurize about twice the pressure of.

Here, the determination of the cantilever control and the both-ports control is performed based on the determinations of steps S1 to S3 as described above, but the cantilever control is performed according to the determination of step S1 is a boom When the control lever for the boom is operated to the boom lowering side, that is, when the working unit 4 is lowered and the boom control lever is not operated to the boom lowering side, that is, when the working unit 4 is stopped moving up and down At the time of ascent, dual control is performed.

In addition, even when the working unit 4 is lowered, the cantilever control is executed according to the determination in step S2 based on the pressure Ph1 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 , The difference between the average value of Ph2 and the pressure Pa of the accumulator 59 is smaller than the set value C1 ({(Ph1 + Ph2) / 2} -Pa <C1), and the set value C1 or more ({(Ph1 + Ph2) In (2)-Pa に は C1), double-end control is executed. Here, the set value C1 is a value set in advance as a differential pressure necessary to cause the pressure oil to flow from the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 to the accumulator 59. If the set value C1 is too small, the lowering speed of the working unit 4 may be slowed, so the heads of the first and second boom cylinders 8 and 9 can be maintained in a state where the lowering speed of the working unit 4 can be secured. The differential pressure necessary for flowing the pressure oil from the side oil chambers 8a and 9a to the accumulator 59 is set as the set value C1. That is, when the differential pressure between the pressure Ph1 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 and the average value of the pressure Ph2 and the pressure Pa of the accumulator 59 is the set value C1 or more, both Even in the holding control, since the discharge oil of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 can be accumulated in the accumulator 59, the cantilever control is not executed. . Incidentally, in order to prevent hunting, the value of the set value C1 is set to be slightly different between when shifting from the double control to the cantilever control and when changing from the cantilever control to the dual control.

Furthermore, even at the time of lowering of the working unit 4, the head side relief pressure Pr2 of the second boom cylinder 9 and the head side oil of the second boom cylinder 9 are subjected to cantilever control according to the determination of step S3. If the differential pressure with the pressure Ph2 of the chamber 9a is larger than the set value C2 (Pr2-Ph2> C2), and if it is less than the set value C2 (Pr2-Ph2 ≦ C2), the both-hand control is executed. Ru. Here, the set value C2 is a value of differential pressure which is set in advance to prevent the inadvertent operation of the second relief valve 38. That is, when the differential pressure between the head-side relief pressure Pr2 of the second boom cylinder 9 and the pressure Ph2 of the head-side oil chamber 9a of the second boom cylinder 9 is less than the set value C2, the second relief valve 38 is not prepared. Since the possibility that the oil in the head side oil chamber 9a of the second boom cylinder 9 flows to the oil tank 12 increases, the cantilever control is not executed.

Next, control of the control device 27 based on the operation of the boom control lever will be described.
First, when the boom control lever is not operated by either the boom lowering side or the raising side, that is, when the working unit 4 is stopped moving up and down, the control device 27 controls the rising side electromagnetic proportional pressure reducing valve 25 and the falling side electromagnetic proportional The control signal of the pilot pressure output is not output to the pressure reducing valve 26, the first electromagnetic proportional pressure reducing valve 35, and the second electromagnetic proportional pressure reducing valve 36, whereby the boom cylinder control valve 18 is positioned at the neutral position N. The first and second flow control valves 33 and 34 are located at the closed position N. Further, the control signal of the flow control signal pressure Pc output is not output to the main pump flow control electromagnetic proportional pressure reducing valve 30, and the negative control signal pressure Pn is input to the regulator 13 of the main pump 10. Further, the cylinder side check valve electromagnetic switching valve 48, the accumulator side check valve electromagnetic switching valve 51, and the tank check valve electromagnetic switching valve 58 are all controlled to be at the OFF position N, whereby the cylinder side check valve 46, the accumulator side check valve 49, and the tank check valve 56 are all kept closed. Furthermore, no operation signal is output to the merging valve electro-hydraulic conversion valve 53, whereby the merging valve 52 is located at the closed position N. Further, when the working unit 4 is stopped moving up and down, as described above, since the both-end control is executed, the head side communication oil passage open / close valve 39 is located at the open position X, and the unload valve 41 is controlled to be in a closed state.

On the other hand, when the boom control lever is operated to the boom lowering side, that is, when the working unit 4 is lowered, as described above, the pressures of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 Depending on Ph1 and Ph2 and the pressure Pa of the accumulator 59, there are cases in which both-port control is performed and in which cantilever control is performed. Then, when the both-ends control is executed, the head side communication oil passage open / close valve 39 is positioned at the open position X, and the unload valve 41 is controlled to be in the closed state. On the other hand, when the cantilever control is executed, the head side communication oil passage open / close valve 39 is located at the closed position N, and the opening area of the first flow control valve 33 is maximized, and furthermore, the unload valve 41 is controlled to be in an open state.

Furthermore, when operated to the boom lowering side, the control device 27 corresponds to the operation amount of the boom control lever at the lowering side pilot port 18b of the boom cylinder control valve 18 with respect to the lowering side electromagnetic proportional pressure reducing valve 26. The control signal is output to output the pilot pressure. As a result, the boom cylinder control valve 18 is switched to the lowering side position Y, so that the pressure oil in the pressure oil supply oil passage 17 becomes the boom cylinder control valve 18 at the lowering position Y and the rod side main oil passage. 24 are supplied to the rod side oil chambers 8b and 9b of the first and second boom cylinders 8 and 9 via the rod side communication oil passage 23. As described later, when the boom control lever is operated to the boom lowering side, only the discharge oil of the main pump 10 is supplied to the pressure oil supply oil passage 17.

Furthermore, when operated to the boom lowering side, the control device 27 does not output a control signal of the flow control signal pressure Pc output to the main pump flow control electromagnetic proportional pressure reducing valve 30. As a result, the pressure input to the other port 29 a of the shuttle valve 29 becomes the tank pressure, and the shuttle valve 29 selects the negative control signal pressure Pn and inputs it to the regulator 13 of the main pump 10. As a result, the main pump 10 is controlled to increase or decrease the discharge flow rate in accordance with the increase or decrease of the operation amount of the boom control lever.

Furthermore, when the boom lowering side is operated, the control device 27 outputs a control signal to the first and second electromagnetic proportional pressure reducing valves 35, 36. The control is different from when cantilever control is performed. First, in the case of dual control, the controller 27 controls the pilot ports 33a and 34a of the first and second flow control valves 33 and 34 with respect to the first and second electromagnetic proportional pressure reducing valves 35 and 36, respectively. A control signal is output so as to output a pilot pressure corresponding to the operation amount of the boom control lever. As a result, the first and second flow control valves 33 and 34 switch to the open position X where the first and second head side oil passages 19 and 20 are opened, and the opening area thereof is the operation amount of the boom control lever It is controlled to correspond to The pressure oil discharged from the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 is recovered via the first and second flow control valves 33 and 34 at the open position X. Although supplied to the oil passage 44, the flow rate is controlled by the opening area of the first and second flow control valves 33, 34. Incidentally, in the case of the both-end control, as described above, the head side communication oil passage open / close valve 39 is positioned at the open position X, and the unload valve 41 is controlled to be closed. The oil discharged from the head-side oil chamber 8a of the boom cylinder 8 and having passed through the first flow control valve 33 does not flow to the oil tank 12 via the head-side discharge oil passage 40, and the head-side communication oil passage 21 Are supplied to the recovery oil passage 44 via the.

Next, the control device 27 controls the pilot pressure corresponding to the operation amount of the boom control lever to the pilot port 34a of the second flow control valve 34 with respect to the second electromagnetic proportional pressure reducing valve 36. Output the control signal. Thereby, the second flow control valve 34 is switched to the open position X where the second head side oil passage 20 is opened. The pressure oil discharged from the head side oil chamber 9a of the second boom cylinder 9 is supplied to the recovery oil passage 44 via the second flow control valve 34 at the open position X, but the flow rate is , And the opening area of the second flow control valve 34. In the case of the cantilever control, as described above, the head side communication oil passage open / close valve 39 is located at the closed position N, and the opening area of the first flow control valve 33 is maximized. The load valve 41 is controlled to be in an open state, whereby the discharge oil from the head side oil chamber 8 a of the first boom cylinder 8 flows to the oil tank 12 via the head side discharge oil passage 40. On the other hand, the oil discharged from the head side oil chamber 9a of the second boom cylinder 9 has a high pressure which is about twice that in the case of dual control, and the high pressure oil is supplied to the recovery oil passage 44. Ru.

Furthermore, when operated to the boom lowering side, the control device 27 outputs a control signal to switch to the ON position X to the cylinder side check valve electromagnetic switching valve 48 and the accumulator side check valve electromagnetic switching valve 51 Do. As a result, the cylinder side check valve 46 and the accumulator side check valve 49 both open, and the flow of oil from the recovery oil passage 44 to the accumulator oil passage 45 is permitted. Thus, in the case of both-end control, the pressure oil discharged from the head- side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 and supplied to the recovery oil passage 44 is also controlled to be cantilevered. In this case, the oil discharged from the head side oil chamber 9a of the second boom cylinder 9 and supplied to the recovery oil passage 44 flows into the accumulator oil passage 45 and is accumulated in the accumulator 59 via the accumulator oil passage 45. It has become so.

Thus, at the time of lowering of the working unit 4, the oil discharged from the head- side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 is accumulated in the accumulator 59 in the both-end control, and cantilevered In the control, oil discharged from the head side oil chamber 9a of the second boom cylinder 9 is accumulated in the accumulator 59. In this case, the oil discharged from the head side oil chambers 8a and 9a is the working portion 4 The dual-arm control that holds the weight of the working unit 4 in both the first and second boom cylinders 8 and 9 by high potential energy of the first and second boom cylinders 8 and 9 is high pressure, and the weight of the working unit 4 in one second boom cylinder 9 In the cantilever control for holding the pressure, the high pressure (about twice) is higher than that in the double control, so that the accumulator 59 stores pressure oil of high pressure that can cope with high load operation.

Furthermore, when the boom lowering side is operated, the control device 27 does not output an operation signal to the merging valve electro-hydraulic conversion valve 53, whereby the merging valve 52 is positioned at the closed position N closing the merging oil passage 16. To be controlled. Thus, only the discharge oil of the main pump 10 is supplied to the pressure oil supply oil passage 17 without the pressure oil being supplied from the accumulator oil passage 45 to the pressure oil supply oil passage 17 via the merging oil passage 16. It has become so.

Further, when the boom lowering side is operated, the control device 27 controls the tank check valve electromagnetic switching valve 58 to be positioned at the OFF position N. Thus, the tank check valve 56 is held in a closed state in which the accumulator discharge oil passage 55 is closed.

Here, when the working unit 4 is lowered, as described above, the oil discharged from the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 is accumulated in the accumulator 59. In this case, in order to prevent the backflow from the accumulator 59 to the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9, the control device 27 controls the first and second head side pressure sensors 62 and 63. Backflow prevention control based on the pressures Ph1 and Ph2 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 input from the second embodiment and the pressure Pa of the accumulator 59 input from the accumulator pressure sensor 64 Is configured to perform. The backflow prevention control is executed when the pressures Ph1 and Ph2 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 are smaller than the pressure Pa of the accumulator 59 at the time of double-end control, and At the time of cantilever control, it is executed when the pressure Ph2 of the head side oil chamber 9a of the second boom cylinder 9 is smaller than the pressure Pa of the accumulator 59. In this case, the control of each valve in the backflow prevention control is as described above. Priority is given to the control of each valve in the dual control and the cantilever control.

When the backflow prevention control is performed, the control device 27 outputs a control signal to switch to the OFF position N to the cylinder side check valve electromagnetic switching valve 48 and the accumulator side check valve electromagnetic switching valve 51. As a result, both the cylinder side check valve 46 and the accumulator side check valve 49 are closed, and the flow of oil from the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 to the accumulator 59, and The flow of oil from the accumulator 59 to the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 is both blocked. Also, a control signal is output to the first and second electromagnetic proportional pressure reducing valves 35 and 36 so as to output a pilot pressure corresponding to the operation amount of the boom control lever, whereby the first and second flow rate control are performed. The valves 33 and 34 are controlled to have an opening area corresponding to the amount of operation of the boom control lever. Further, a control signal is output to the head side communication oil path on-off valve 39 so that the head side communication oil path 21 is positioned at the open position X, and the unload valve electromagnetic switching valve 43 is turned on. A control signal is output so as to be located at the position X, whereby the unload valve 41 is in an open state in which the head side discharge oil passage 40 is opened. Then, the first and second flow control valves 33 and 34 are opened, the head side communication oil passage 21 is opened, and the head side discharge oil passage 40 is further opened. Exhaust oil from the head side oil chambers 8a and 9a flows to the oil tank 12 in a state where the flow rate is controlled by the first and second flow rate valves 33 and 34.

That is, when the backflow prevention control is executed when the working unit 4 is lowered, the head side oil of the first and second boom cylinders 8 and 9 is detected by the cylinder side check valve 46 and the accumulator side check valve 49 in the closed state. The flow of oil from the chambers 8a, 9a to the accumulator 59 and the flow of oil from the accumulator 59 to the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 are blocked, The pressure oil in the head side oil chambers 8a and 9a of the two boom cylinders 8 and 9 is discharged to the oil tank 12 in a state where the flow rate is controlled by the first and second flow control valves 33 and 24.
When the both-end control is performed when the working unit 4 is lowered, the head-side relief pressure Pr2 of the second boom cylinder 9 and the second boom cylinder 9 are determined by the determination of the both-end control and the cantilever control described above. The pressure Ph1 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 except when the differential pressure with the pressure Ph2 of the head side oil chamber 9a is less than or equal to the set value C2 (Pr2-Ph2 ≦ C2) When the differential pressure between the average value of Ph2 and the pressure Pa of the accumulator 59 becomes smaller than the set value C1 ({(Ph1 + Ph2) / 2} -Pa <C1), the control shifts from the dual control to the cantilever control. Therefore, there is a possibility that the backflow prevention control may be executed at the time of double-end control, the head-side relief pressure Pr2 of the second boom cylinder 9 and the pressure Ph2 of the head-side oil chamber 9a of the second boom cylinder 9 Only when the differential pressure is less than the set value C2.
Further, in the present embodiment, the first and second head side oil passages 19 and 20, the head side communication oil passage 21, the head side communication oil passage on-off valve in which the first and second flow control valves 33 and 34 are disposed. 39, the head side discharge oil passage 40, and the unload valve 41, oil discharged from the head side oil chamber of the first and second hydraulic cylinders of the present invention through the first and second flow control valves Constitute a freely openable and closable tank oil passage. That is, in the present embodiment, the head side communication oil passage 21, the head side communication oil passage on-off valve 39, the head side discharge oil passage 40, and the unloading valve 41 used when performing double-end control and cantilever control are used as they are. By using this, a freely openable and closable tank oil passage is formed when backflow prevention control is performed, thereby simplifying the circuit.

Next, when the boom control lever is operated to the boom raising side, that is, the control when the working unit 4 is lifted, as described above, when the working unit 4 is lifted, the both-end control is performed Therefore, the head side communication oil passage open / close valve 39 is positioned at the open position X, and the unload valve 41 is controlled to be in the closed state.

Furthermore, when operated to the boom rising side, the control device 27 corresponds to the operation amount of the boom control lever at the upper and lower pilot ports 18 a of the boom cylinder control valve 18 with respect to the rising electromagnetic proportional pressure reducing valve 25. The control signal is output to output the pilot pressure. As a result, the boom cylinder control valve 18 is switched to the rising side position X, and the pressure oil in the pressure oil supply oil passage 17 is firstly transmitted via the boom cylinder control valve 18 at the rising side position X. The oil is supplied to the head side oil chambers 8 a and 9 a of the second boom cylinder 8 and the discharge oil from the rod side oil chambers 8 b and 9 b is discharged to the oil tank 12. As described later, not only the discharge oil of the main pump 10 but also the pressure-accumulated oil of the accumulator 59 is supplied to the pressure oil supply oil passage 17 when operated to the boom upward side.

Furthermore, at this time, the control device 27 does not output the control signal of the pilot pressure output to the first and second electromagnetic proportional pressure reducing valves 35, 36, whereby the first and second flow control valves 33, 34 It is controlled to be located at the closed position N. Further, as described above, the head side communication oil passage open / close valve 39 is located at the open position X, and the unload valve 41 is in the closed state. The pressure oil supplied to the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 via the boom cylinder control valve 18 at the rising side position X is the head side discharge oil. The head side main oil passage 22, the head side communication oil passage 21, and the first and second check valves 31 of the first and second head side oil passages 19 and 20 without flowing into the oil tank 12 via the passage 40. , 32 to reach the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 respectively.

Furthermore, when operated to the boom rising side, the control device 27 controls the cylinder side check valve electromagnetic switching valve 48 and the accumulator side check valve electromagnetic switching valve 51 to be positioned at the OFF position N. As a result, the cylinder side check valve 46 and the accumulator side check valve 49 are held in the closed state, and thus the state between the collection oil passage 44 and the accumulator oil passage 45 is shut off.

Furthermore, when operated to the boom rising side, the control device 27 outputs an operation signal to the merging valve electro-hydraulic conversion valve 53 so as to switch the merging valve 52 to the open position X. Thereby, the merging valve 52 opens the merging oil passage 16 from the accumulator oil passage 45 to the discharge line 15 of the main pump 10, but the opening area thereof is the operation amount of the boom control lever and the pressure Pa of the accumulator 59 and the main It is controlled according to the differential pressure with the discharge pressure Pp of the pump 10. Then, the pressure oil accumulated in the accumulator 59 joins the discharge line 15 of the main pump 10 via the accumulator oil passage 45 and the joining oil passage 16 and, as described above, the pressure oil supply oil passage The head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 are supplied via the boom cylinder control valve 18 at the rising position X17.

Furthermore, when operated to the boom rising side, the control device 27 outputs a control signal to the main pump flow control electromagnetic proportional pressure reducing valve 30 so as to output the flow control signal pressure Pc. In this case, the control device 27 sets the discharge flow rate of the main pump 10 to a flow rate obtained by subtracting the merging amount from the accumulator 59 from the pump flow rate required according to the operation amount of the boom operation lever and the pump output. To control the value of the flow control signal pressure Pc.

The flow control signal pressure Pc output from the main pump flow control electromagnetic proportional pressure reducing valve 30 is input to the other input port 29 b of the shuttle valve 29. On the other hand, the negative control signal pressure Pn is input to one input port 29a of the shuttle valve 29, but in the state where the supply pressure oil from the accumulator 59 joins the discharge line 15, the flow control signal pressure Pc is Is a signal pressure that makes the pump flow smaller than the negative control signal pressure Pn, that is, the flow control signal pressure Pc is higher than the negative control signal pressure Pn, so the flow control signal pressure Pc is selected by the shuttle valve 29 And is input to the regulator 13 of the main pump 10. Thus, the discharge flow rate of the main pump 10 is controlled to be a flow rate reduced by the amount of merging from the accumulator 59.

That is, when the working unit 4 ascends, the pressure-accumulated oil of the accumulator 59 joins with the discharge oil of the main pump 10 via the joining oil passage 16 and the joined pressure oil is the boom cylinder control valve at the rising position X It is supplied to the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 via the line 18. Further, at this time, the discharge flow rate of the main pump 10 is controlled to be a flow rate reduced by the amount of merging from the accumulator 59. Thus, the potential energy collected by the accumulator 59 when the working unit 4 is lowered can be reused when the working unit 4 is raised, and the discharge flow rate of the main pump 10 can be reduced accordingly. .

Furthermore, when the boom raising side is operated, the control device 27 controls the tank check valve electromagnetic switching valve 58 to be positioned at the OFF position N. Thus, the tank check valve 56 is held in a closed state in which the accumulator discharge oil passage 55 is closed.

Next, accumulator discharge control performed by the control device 27 will be described.
The controller 27 switches the tank check valve electromagnetic switching valve 58 to the ON position X for a predetermined time when the operator operates an accumulator discharge operation switch (not shown) or when the engine E is stopped. As a result, the tank check valve 56 is opened to open the accumulator discharge oil passage 55, and the accumulated oil of the accumulator 59 is discharged to the oil tank 12 via the accumulator discharge oil passage 55. . That is, when the accumulator discharging operation switch is operated or the engine E is stopped, the accumulated oil of the accumulator 59 is automatically drained to the oil tank 12 to be in a state suitable for long-term storage. Even when the shovel 1 is not used for a long time, it is possible to reliably avoid such a problem that the accumulator 59 is left for a long time with oil accumulated in the accumulator 59 for a long time and the gas amount of the accumulator 59 decreases. There is.

Further, when the engine E is stopped, the controller 27 controls the cylinder side check valve electromagnetic switching valve 48, the accumulator side check valve electromagnetic switching valve 51, and the tank check valve electromagnetic switching valve 58 for a predetermined time. The first and second proportional proportional pressure reductions are made so that the first and second flow control valves 33, 34 can be switched to the open position X based on the downward operation of the boom control lever while switching to the ON position X Control the valves 35, 36. Thus, based on the downward operation of the boom control lever, the oil of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 is collected into the recovery oil passage 44, the accumulator oil passage 45, and the accumulator. It is possible to flow to the oil tank 12 via the discharge oil passage, whereby the working unit 4 is operated based on the descent side operation of the boom control lever for a predetermined time even after the stop operation of the engine E. Can be lowered.

In the present embodiment configured as described above, the working unit 4 of the hydraulic shovel 1 ascends and descends as the boom 5 constituting the working unit 4 moves up and down. The hydraulic control system of the hydraulic shovel 1 includes the first boom cylinder of one of the pair of first and second boom cylinders 8 and 9 although the expansion control of the second boom cylinders 8 and 9 is performed. An open / close unload oil passage (first head side oil passage 19, first flow control valve 33, head side discharge oil passage 40, and unload valve) for flowing pressure oil of the head side oil chamber 8 a into the oil tank 12 41 and a controller 27 for controlling the opening and closing of the unloading oil passage, and in the state where the unloading oil passage is closed, the first and second boom cylinders 8 are provided. , 9 heads While the weight of the working unit 4 is held by the pressure of the side chambers 8a and 9a, the unloading oil passage is open (the opening area of the first flow control valve 33 is maximum and the unloading valve 41 is open) In this case, the pressure of the head side oil chamber 9a of the second boom cylinder 9 holds the weight of the working unit 4 and the first and second of holding the weight of the working unit 4 when the working unit 4 is lowered. The oil discharged from the head side oil chambers 8a, 9a of the boom cylinders 8, 9 or the head side oil chamber 9a of the second boom cylinder 9 is accumulated in the accumulator 59.

Thus, when the working unit 4 is lowered, the unloading oil passage is opened and the pressure oil of the head side oil chamber 8a of the first boom cylinder 8 flows to the oil tank 12, whereby the weight of the working unit 4 is the second boom The oil is held by the pressure of the head side oil chamber 9a of the cylinder 9, and the oil discharged from the head side oil chamber 9a of the second boom cylinder 9 is accumulated in the accumulator 59. In this case, the second boom The pressure of the head side oil chamber 9a of the cylinder 9, that is, the holding pressure for holding the weight of the working unit 4 is the holding pressure when the weight of the working unit 4 is held by both the first and second boom cylinders 8,9. Therefore, the accumulator 59 is charged with high pressure oil which can cope with high load operation.

As a result, the accumulator 59 can store high-pressure hydraulic oil that can cope with high-load operations such as digging work and lifting and turning, so that the pressure-accumulated oil of the accumulator 59 can be used as it is without separately boosting pressure. It will be available for work. Thus, as in the case of increasing the pressure-accumulated oil of the accumulator using a pump driven by the engine power, the torque reduction in the power transmission path from the engine to the pump, the loss of idling torque due to the inertia mass of the pump itself, etc. In addition, the potential energy of the working unit 4 collected in the accumulator 59 can be used with as little loss as possible, and can greatly contribute to cost reduction.

Further, in the hydraulic control system of the hydraulic shovel 1, a head side communication oil passage 21 communicating the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 with each other, and the head side communication oil passage 21 A head side communication oil passage open / close valve 39 controlled by the control device 27 for opening and closing is provided, and the head side communication oil passage on / off valve 39 is in a state where the unloading oil passage is closed. While the oil passage 21 is opened, the head side communicating oil passage 21 is controlled to be closed when the unloading oil passage is open. Thus, in the state where the unloading oil passage is closed, that is, both-end control for holding the weight of the working unit 4 in the head side oil chambers 8a and 9a of both the first and second boom cylinders 8 and 9 is performed. In the state of being executed, both head side oil chambers 8a and 9a are in communication with each other, and the work unit 4 can be supported in a well-balanced manner by the pair of first and second boom cylinders 8 and 9, while the unloading oil passage In the open state, that is, in the state where cantilever control for holding the weight of the working unit 4 in the head side oil chamber 9a of the second boom cylinder 9 is performed, the head side oil chamber of the second boom cylinder 9 Thus, it is possible to shut off the head oil chamber 8a of the first boom cylinder 8 from the head cylinder 9a.

Further, the unloading oil passage is opened, that is, the cantilever control is executed when the working unit 4 for accumulating pressure in the accumulator 59 descends, and when the working unit 4 is stopped moving up and down, and when lifting Since the load oil passage is closed, that is, both-end control is executed, the pressure oil in the head side oil chamber 8a of the first boom cylinder 8 is used except when accumulating pressure in the accumulator 59. The loss flowing to the oil tank 12 can be eliminated, and there is no fear that the power will be insufficient or the balance will be lost when the working unit 4 is raised.

Furthermore, in this device, even when the working unit 4 is lowered, the average value of the pressures Ph1 and Ph2 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 and the pressure Pa of the accumulator 59 When the differential pressure is equal to or greater than the set value C1 ({(Ph1 + Ph2) / 2} -Pa ≧ C1), the unload oil passage is closed, that is, both-hand control is performed, and the first and second boom cylinders The oil discharged from the head side oil chambers 8 a and 9 a of 8 and 9 is accumulated in the accumulator 59. Thus, the pressures Ph1 and Ph2 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 are higher than the pressure Pa of the accumulator 59, and can be accumulated in the accumulator 59 even by double control. In this case, the cantilever control will not be executed, which causes the pressure oil in the head side oil chamber 8a of the first boom cylinder 8 to flow to the oil tank 12 when the unloading oil passage is opened. It can be reduced.

Furthermore, in this case, even when the working unit 4 is lowered, the differential pressure between the head-side relief pressure Pr2 of the second boom cylinder 9 and the pressure Ph2 of the head-side oil chamber 9a of the second boom cylinder 9 is a set value In the case of C2 or less (Pr2-Ph2 ≦ C2), the unload oil passage is closed, that is, both-end control is performed. As a result, the pressure Ph2 of the head-side oil chamber 9a of the second boom cylinder 9 can be prevented from rising excessively and the second relief valve 38 can be prevented from inadvertently operating. It is possible to eliminate the loss that the oil discharged from the head side oil chamber 9 a of the second boom cylinder 9 flows to the oil tank 12 by operating the valve 38.

Further, in the hydraulic control system of the hydraulic shovel 1, the first and second flow rate control for controlling the discharge flow rate from the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 when the working unit 4 descends. Valves 33 and 34 are provided, and the lowering speed of the working unit 4 can be controlled by the first and second flow control valves 33 and 34 at the time of double control or cantilever control.

Further, the hydraulic control system of the hydraulic shovel 1 includes a cylinder side check valve 46 capable of blocking the flow of oil from the head side oil chambers 8 a and 9 a of the first and second boom cylinders 8 and 9 to the accumulator 59. Because an accumulator side check valve 49 capable of blocking the flow of oil from the accumulator 59 to the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 is provided, these cylinder side checks The pressure oil of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 flows out to the accumulator 59 when the elevation of the working unit 4 is stopped by the valve 46 and the accumulator side check valve 49, or The problem is confirmed that 59 stored pressure oil is supplied to the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9, respectively. It can be avoided.

Furthermore, when the working unit 4 descends, when the pressures Ph1 and Ph2 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 are smaller than the pressure Pa of the accumulator 59 at the time of double control, When the pressure Ph2 of the head side oil chamber 9a of the second boom cylinder 9 is smaller than the pressure Pa of the accumulator 59 at the time of the cantilever control, the backflow prevention control is executed. That is, by the cylinder side check valve 46 and the accumulator side check valve 49, the flow of oil from the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 to the accumulator 59, and , The flow of oil to the head side oil chambers 8a, 9a of the second boom cylinders 8, 9 is blocked, and the oil discharged from the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 is It flows to the oil tank 12 in a state in which the flow rate is controlled by the first and second flow control valves 33 and 34. Even when the pressures Ph1 and Ph2 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 transiently become smaller than the pressure Pa of the accumulator 59 when the working unit 4 is lowered, the accumulator The pressure oil can be reliably prevented from backflowing from 59 to the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9, and even in this case, the first, The working unit 4 can be lowered with the speed controlled by the two flow control valves 33 and 34.

The present invention is, of course, not limited to the above-described embodiment, and in the above-described embodiment, the pressure-accumulated oil of the accumulator 59 is merged with the discharge line 15 of the main pump 10 via the merging oil passage 16 The configuration is such that the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 are supplied when the working unit 4 ascends, but the invention is not limited thereto. Can also be used as supply pressure oil to a plurality of other hydraulic actuators provided in the work machine (in the case where the work machine is a hydraulic shovel, a traveling motor, a swing motor, an arm cylinder, a bucket cylinder, etc.). In this case, the potential energy recovered when the working unit 4 is lowered can be used for the operation of other hydraulic actuators.
Furthermore, the present invention can be applied not only to hydraulic excavators, but also to hydraulic control systems of various working machines provided with a pair of hydraulic cylinders that raise and lower the working unit.
Further, in the hydraulic circuit diagram of FIG. 2, one main pump is shown as a hydraulic pump for supplying pressure oil to a plurality of hydraulic actuators, but it goes without saying that two or more main pumps may be provided.

The present invention relates to the technical field of a hydraulic control system in a working machine capable of recovering and reusing potential energy of the working unit in a working machine provided with a vertically movable working unit, and configured as in the present invention By opening the unloading oil passage and letting the pressure oil in the head-side oil chamber of the first hydraulic cylinder flow to the oil tank by lowering the working part, the accumulator can be used for high-load operations. The pressure oil is accumulated, and the pressure accumulation oil of the accumulator can be used for various operations without using additional pressure increase. In addition, the potential energy of the working unit collected in the accumulator can be used with as little loss as possible, and can greatly contribute to cost reduction. In addition, it is possible to eliminate the loss that the pressure oil in the head-side oil chamber of the first hydraulic cylinder flows to the oil tank except at the time of descent of the working unit for accumulating pressure in the accumulator. In the industry, there is a possibility that there is no fear of losing power or losing balance.

4 Working part 8 First boom cylinder 8a First boom cylinder head side oil chamber 9 Second boom cylinder 9a Second boom cylinder head side oil chamber 12 Oil tank 19 First head side oil passage 21 Head side communicating oil passage 27 Control device 33 1st flow control valve 34 2nd flow control valve 38 2nd relief valve 39 head side communication oil path on-off valve 40 head side discharge oil path 41 unload valve 46 cylinder side check valve 49 accumulator side check valve 59 accumulator 62 first Head side pressure sensor 63 Second head side pressure sensor 64 Accumulator pressure sensor

Claims (8)

1. In a hydraulic control system of a working machine comprising a vertically movable work unit and a pair of first and second hydraulic cylinders that raise and lower the work unit, the hydraulic control system includes a head side oil chamber of the first hydraulic cylinder. A unloadable oil passage that allows pressure oil to flow to the oil tank and a control device that controls the opening and closing of the unload oil passage are provided, and when the unload oil passage is closed, the first and second hydraulic cylinders While the weight of the working unit is held by the pressure of the head side oil chamber, the weight of the working unit is held by the pressure of the head side oil chamber of the second hydraulic cylinder while the unloading oil passage is open. An oil pressure control system in a working machine characterized by comprising an accumulator for accumulating oil discharged from a head side oil chamber of a first and second or second hydraulic cylinder for holding weight when the working part is lowered. Beam.
2. In the hydraulic control system, a head side communication oil passage communicating head side oil chambers of the first and second hydraulic cylinders, and a head side communication oil passage opened and closed by the control device to open and close the head communication passage. The control device is provided with a valve, and the controller opens the head side communication oil passage when the head side communication oil passage opening / closing valve is closed, and the head when the unloading oil passage is open. The hydraulic control system in a working machine according to claim 1, wherein control is performed to close the side communication oil passage.
3. The work machine according to claim 1 or 2, wherein the control device controls to open the unloading oil passage when the working unit descends and close the unloading oil passage when the elevation of the working unit is stopped and rising. Hydraulic control system in the.
4. The hydraulic control system is provided with accumulator pressure detection means for detecting the pressure of the accumulator, and first and second head side pressure detection means for detecting the pressure of the head side oil chambers of the first and second hydraulic cylinders, respectively. Even when the working unit is lowered, the control device is configured to set the differential pressure between the average pressure of the head side oil chambers of the first and second hydraulic cylinders and the pressure of the accumulator to a preset value or more. The hydraulic control system in a working machine according to claim 3, wherein the control is performed to close the unloading oil passage.
5. The hydraulic control system is provided with second head pressure detection means for detecting the pressure in the head oil chamber of the second hydraulic cylinder, and a second relief valve for setting the head relief pressure of the second hydraulic cylinder, and control In the device, even when the working unit is lowered, the differential pressure between the head-side relief pressure of the second hydraulic cylinder and the pressure of the head-side oil chamber of the second hydraulic cylinder is equal to or less than a preset value set in advance. The hydraulic control system in a working machine according to claim 3 or 4, wherein control is performed to close the unloading oil passage.
6. The hydraulic control system is provided with a first flow control valve and a second flow control valve for controlling the discharge flow rate from the head side oil chamber of the first and second hydraulic cylinders at the time of lowering of the working unit. The hydraulic control system in the working machine according to any one of 5.
7. In the hydraulic control system, blocking the flow of oil from the head side oil chamber of the first and second hydraulic cylinders to the accumulator and the flow of oil from the accumulator to the head side oil chamber of the first and second hydraulic cylinders A hydraulic control system in a working machine according to any one of claims 1 to 6, characterized in that a valve means is provided.
8. The hydraulic control system includes: accumulator pressure detection means for detecting the pressure of the accumulator; first and second head side pressure detection means for respectively detecting the pressure of the head side oil chambers of the first and second hydraulic cylinders; An openable / closable tank oil passage for flowing oil discharged from the head side oil chamber of the second hydraulic cylinder to the oil tank via the first and second flow control valves, and the head side oil chamber of the first and second hydraulic cylinders And the valve means capable of blocking the flow of oil from the accumulator to the accumulator and the flow of oil from the accumulator to the head side oil chambers of the first and second hydraulic cylinders, and the control device , When the pressure in the head side oil chamber of the first and second or second hydraulic cylinders holding weight is smaller than the pressure of the accumulator, the valve means The oil flow from the fuel side oil chamber to the accumulator and the oil flow from the accumulator to the head side oil chambers of the first and second hydraulic cylinders are blocked, and the tank oil passage is opened to The hydraulic control system in a working machine according to claim 6, wherein the pressure oil in the head side oil chamber of the hydraulic cylinder is caused to flow to the oil tank via the first and second flow control valves.

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